The invention relates to methods for etching features in a semiconductor substrate, including etching features in silicon.
The fabrication of integrated circuits (IC) in the semiconductor industry typically involves using a plasma reactor to create plasma that assists surface chemistry used to remove material from—and deposit material to—a substrate. Dry plasma etching processes are routinely used to remove or etch material along fine lines or within vias or at contacts patterned on a semiconductor substrate. A successful plasma etching process requires an etching chemistry that includes chemical reactants suitable for selectively etching one material while substantially not etching another material.
For example, on a semiconductor substrate, a pattern formed in a protective layer can be transferred to an underlying layer of a selected material using a plasma etching process. The protective layer can comprise a light-sensitive layer, such as a photoresist layer, having a pattern formed using a lithographic process. Once the pattern is formed, the semiconductor substrate is disposed within a plasma processing chamber, and an etching chemistry is formed that selectively etches the underlying layer while minimally etching the protective layer. This etch chemistry is produced by introducing an ionizable, dissociative gas mixture having parent molecules comprising molecular constituents that react with the underlying layer while minimally reacting with the protective or patterning layer. Production of the etch chemistry comprises introduction of a gas mixture and formation of plasma when a portion of the gas species present are ionized following a collision with an energetic electron. Heated electrons can serve to dissociate some species of the gas mixture and create a reactive mixture of chemical constituents (of the parent molecules).
With ionized gas species and a reactive mixture of chemical constituents provided, various features (e.g., trenches, vias, contacts, etc.) can be etched in exposed regions of the semiconductor substrate. Typical materials that are etched include silicon oxide (SiOx), silicon nitride (SiNy), poly-crystalline silicon (polysilicon), mono-crystalline silicon (silicon), and doped and un-doped silicon, for example.